This invention relates generally to electroluminescent lamps and more particularly to an improved method and structure for making electrical connections to an electroluminescent lamp from only one side of the lamp.
Electroluminescent lamps are generally constructed as laminated or layered structures. Electroluminescent lamps function by application of an electrical potential to two conductive layers separated by an electroluminescent layer, which may comprise electroluminescent particles fixed in a resin binder.
Electroluminescent lamps have been modified to provide a lighted watch dial, as disclosed in U.S. Pat. No. 4,775,964 issued Oct. 4, 1988 to Alessio et al and assigned to the present assignee. While it is easy to make one of the electrical contacts to the back electrode comprising a conductive area on the underside of the electroluminescent watch dial, it is more difficult to make the other electrical contact to the front electrode, since this is a conductive layer which is embedded between other layers. Therefore, it has been necessary to either omit a part of the electroluminescent material to expose the front electrode, as shown in the aforesaid Alessio et al patent, or to provide a special overlap area extending beyond the normal periphery of the lamp.
An improved electroluminescent watch dial support and connector assembly is shown in U.S. Pat. No. 5,265,071 issued Nov. 23, 1993 and assigned to the present assignee, employing special tabs extending beyond the dial periphery for making electrical contact. However, it would be desirable to make electrical contact to both of the electroluminescent electrodes from any location on the back of the EL lamp without regard to the location of the lamp periphery.
It should be recognized that wherever electroluminescent material is missing, there is an objectionable dark spot on the lamp, since there are no electroluminescent particles to luminesce. In the case of an electroluminescent watch dial, it is preferable that the entire area used for observing the timekeeping numbers or other indicia be lighted without the presence of such a dark spot. However, there are some areas near the center of the watch dial in which a dark spot may be permitted without interfering noticeably with the aesthetic qualities of the timepiece. In U.S. Pat. No. 5,346,718 issued Sep. 13, 1994 and assigned to the present assignee, a process of manufacturing an electroluminescent watch dial is disclosed in which the dark spot could be located wherever desired, and which also permits electrical connection to both front and back electrodes from any location on the rear of the electroluminescent watch dial. Nonetheless, it would be desirable to make electrical contact to both of the electroluminescent electrodes from any location on the back of the EL lamp with the dark spot minimized to virtual nonexistence.
Accordingly, it is the object of the present invention to provide an improved electroluminescent lamp and method of making the same in which electrical contacts are permitted from any location on one side of the lamp with the dark spot minimized to near elimination.